Field of the Disclosure
The present disclosure relates to variable apertures, and more specifically, to time-varying and transparency-varying apertures.
Background
Typically, an iris in a lens forms an aperture that closes down to change the amount of light going through the imaging system. The iris can sometimes be completely closed to act as a shutter.
FIG. 1 is a diagram of a conventional lens system 100 including various lens or optical elements 110, 112, 114, 116 and an iris 120. In FIG. 1, the light rays 140 incident on the lens elements 110, 112 pass through the iris 120 and the lens elements 114, 116 and falls on an image sensor 142.
The blades 122 of the iris 120 form an opening or aperture 130. The shape of the iris opening (or the aperture) also affects the image rendition. Term “aperture” may be used interchangeably with “iris”. In FIG. 1, the shape of the aperture may have pointed edges 124. For example, having an aperture that has pointed edges (typical of most lenses) may result in star patterns for strong light sources, or out-of-focus areas being nervously-detailed rather than having smooth bokeh. This may be undesirable for certain purposes. Thus, a round aperture, which may result in relatively round out-of-focus discs in a more pleasingly-rendered bokeh, may be desirable. Towards that goal, the lens designers often increase the number of blades to improve on the circular shape of the aperture formed by the blades. However, adding blades adds complexity to the lens system and may cause unanticipated operational problems.
Further, the bokeh is often not just a function of the aperture shape, but also of the optics. Thus, even if the aperture shape is substantially circular, the lens design itself may result in a bad bokeh. For example, a harsh bokeh is often generated when out-of-focus rings have more noticeable outer rims or rings inside the disc. To counter this problem, some lenses may include an apodisation filter near the aperture to soften the edges of the disc. An apodisation filter is similar to a neutral density filter configured to attenuate more light in areas that are farther away from the center of the aperture. However, such a filter is normally designed for one aperture size. Therefore, the filter would need to be changed as other parameters change, such as changing the aperture size, the focal length (in a zoom lens) or the focusing distance of the imaging system.